In situ combustion



United States Patent f IN SIT U COMBUSTION Allen D. Garrison, La Jolta, 'Calif., and Robert E.

Kunetkml-Iouston, Tex., assignors to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Application November 29, 1956 Serial No. 624,999

6 Claims. (Cl. 166-38) This invention relates to production of petroleum from underground petroleum producing formations. More particularly, this invention relates to carrying out an in situ combustion operation within an underground petroleum producing formation.

Various techniques have been proposed for the recovery of petroleum from underground formations and for the treatment of petroleum producing formations. For the recovery of petroleum from petroleum producing formations secondary recovery operations which involve water flooding or thermal recovery methods, in situ combustion, employing at least one injection well and at least one production well have been proposed. In situ combustion has also been proposed as a well remedial treatment to improve the permeability and/ or porosity of a petroleum producing formation.

In an in situ combustion operation a high temperature zone is established in the petroleum producing formation in the vicinity of the well bore by suitable heating means. Suitable heating means may comprise an electrical heating device or a gas fired bottom hole igniter or heater. A suitable device for initiating in situ combustion within a bore hole is described in U. S. 2,722,278. Another technique or method involving spontaneous combustion for initiating in situ combustion is described in U. S. 2,747,672.

Upon introducing a combustion supporting or an oxygen-containing gas, such as air, into the thus-heated petroleum producing formation via the well bore a high temperature zone, temperature in the range 700-2500 F., usually in the range 800-l750 F., created by the reaction between the oxygen and combustible residues within the formation, such as combustible residues resulting from the distillation and/ or thermal cracking of the crude oil originally in place or introduced thereinto, will commence to move into the formation outwardly from the well bore in the direction of flow of the hot gaseous combustion products.

Leaving this high temperature zone is a relatively high temperature gas stream at substantially the same temperature which, as it moves outwardly into the formation, loses heat to the formation. By this method the high temperature reaction zone is moved radially outwardly from the Well bore Without further direct application of heat to the area immediately surrounding the Well bore. The distance the high temperature reaction zone moves outwardly, and accordingly the volume of the petroleum producing formation swept by or comprised within the high temperature in situ combustion zone, is determined by the relative magnitudes of the rate of heat generation (combustion of combustible residues) and the rate of heat loss to the surrounding formation.

It has been postulated that the following mechanisms are important in an underground in situ combustion operation for the movement of the high temperature zone radially outwardly from the well bore into the petroleum producing formation. Although the exact mechanism of in situ combustion is not definitely completely known, the

following sequence of events in an underground in situ combustion operation is postulated and is presented herein for the purpose of enabling one skilled in the art to better understand the practice of this invention and is not to be construed as limiting this invention in any way.

As the high temperature reaction zone approaches a given volume of the petroleum hydrocarbon-containing formation the temperature of this volume of formation rises. This results in a reduction in the viscosity of the formation fluids therein due to their temperature increase. These fluids may then be moved more readily under the influence of the hot gas stream continuously emanating from the high temperature reaction or combustion zone. As the temperature of this volume of formation continues to rise distillations of the liquids therein begin. The products of these distillations condense in cooler regions of the formation removed from the high temperature combustion zone in the direction of gas flow. These distillations continue as the temperature rises until the heavier components remaining from the petroleum hydrocarbons originally in place within the formation or introduced therein prior to effecting in situ combustion begin to crack or otherwise thermally decompose yielding hydrocarbon gases, coke and similar solid carbonaceous residues. As the temperature continues to rise and the oxygen content of the incoming gas to the given volume of formation increases due to depletion of combustible residues in preceding regions or volumes of the formation, a point will be reached at which the coke or other combustible residues will begin to chemically combine with the oxygen with resulting release of heat to the formation and the gas stream emanating therefrom. This heat is carried away by the onmovin'g gas stream and also to a limited extent by conduction to the adjacent regions of the formation. When the coke or combustible residues have been burned away there remains a volume of substantially liquid-free formation which, unless otherwise treated, is then gradually cooled by the relatively cool combustion supporting gas or air entering the thus-treated given portion of the formation via the well bore.

From the above-indicated considerations it is obvious that the rate of heat energy released within the formation should be some function of the quantity of fuel or combustible residues present therein, which is dependent upon type and quantity of the petroleum originally inplace and/or combustible material or fuel caused to be deposited within the formation in the zone of in situ combustion. Therate of heat releasedis also dependent upon. the rate at which oxygen is supplied to the combustion zone or, in other Words, the rate at which the exothermic combustion process Within the formation undergoing treatment is effected. The rate at which heat can be transferred ahead of the high temperature reaction or combustion zone should be dependent on the rate at which the gaseous products of combustion leave the high temperature combustion or reaction zone and should be tosome extent dependent upon conduction through the formation itself. Accordingly, some control of the in situ combustion process can be exercised by controlling or promoting the oxidation or combustion process occurring with the in situ combustion operation.

Accordingly, it is an object of this invention to provide I an improved method for the treatment of petroleumcontaining or producing formations to enhance or otherwise improve the recovery of petroleum therefrom by an operation involving in situ combustion.

It is another object of this invention to provide an improved process for carrying out an in situ combustion operation.

Still another object of this invention is to provide a. method for initiating and/ or maintaining an under-ground in situ combustion operation.

Yet another object of this invention is to provide a method-for promoting or improving an in situ combustion operation wherein elemental 'oxygen is employed to oxidize combustible residues within a porous subterranean formation.

How these and other objects of this invention are accomplished will become apparent with reference to the accompanying disclosure. In at least one embodiment of the practice of this invention at least one of the foregoing objects will be achieved.

In accordance with the practice of this invention an in situ combustion operation, wherein carbonaceous materials or residues within a porous subterranean formation are contacted with elemental oxygen to oxidize the same, improved combustion or oxidation is effected by carrying out the in situ combustion or oxidation process in the presence of an oxidation catalyst introduced into the formation.

Various oxidation catalysts may be employed in the practice of this invention. Particularly suitable oxidation catalysts are compounds, preferably water-soluble inorganic compounds, containing the element potassium, sodiurn, lithium, barium or calcium. One or more of these elements may be present in the compound. Suitable oxi dation catalysts include the hydroxides and the salts of these metals, particularly the carbonates thereof, viz., lithium hydroxide, potassium hydroxide, sodium hydroxide, barium hydroxide, calcium hydroxide, potassium carbo nate, sodium carbonate, lithium carbonate, barium carbonate, calcium carbonate and others.

The subject invention may be practiced in a single well or a multi-well in situ combustion operation. In a single well in situ combustion operation as set forth in copending, coassigned patent application Serial No. 576,486, filed April 5, 1956, in the name of Gerhard Herzog, there is described a single well in situ combustion operation as a remedial treatment to increase the productivity and/or permeability of an underground petroleum producingor petroleum-containing formation. The practice of this invention is particularly applicable to a well remedial treatment since by following the practice of this invention the zone surrounding a single well bore can readily be subjected to in situ combustion, the same well bore serving as a conduit not only for the introduction of the oxidation catalyst, preferably dissolved in an aqueous solution or in solution or suspension in a hydrocarbon fraction, into the formation in which in situ combustion is to be carried out, but also as a conduit for the introduction of the elemental oxygen, usually in the form of air, into the formation.

The practice of this invention is particularly desirable in an in situ combustion operation wherein a plurality of wells, that is, at least one injection well and at least one production well, is employed. In a multi-well system, and even in a single well system, the radial extent of the .in situ combustion zone from the initial point of the in situ combustion can be greatly extended as compared with an in situ combustion operation carried out with the benefits of the practice of this invention.

Exemplary of the practice of this invention an aqueous solution of a potassium carbonate was introduced into a bed of packed sand containing finely divided coke substantially uniformly distributed therethrough. In situ combustion was established within the bed of packed sand and continued for a suitable period of time. Upon inspection of the sand bed after the in situ combustion operation was terminated it was observed that the amount of coke residue after in situ combustion was materially reduced as compared with a similar in situ combustion operation carried out therein in the absence of the added oxidation catalyst (potassium carbonate).

Further exemplary of the practice of this invention a concentrated aqueous solution of an alkali metal hydroxide, such as potassium hydroxide, lithium hydroxide and/ or sodium hydroxide, is introducedinto a subsurface petroleum-containing formation in a volume sufiicient to displace the formation Water or brine therein for a substantial radial distance surrounding the well bore, e. g., an amount of solution suflicient to displace the formation water or brine for a distance of 3-25 radial feet from the well bore. Thereafter a bottom hole igniter is introduced into the well bore and located adjacent the thustreated petroleum-containing formation. That section of the formation immediately surrounding the well bore is heated to a temperature of at least about 750 F., preferably in the range 800-1300" F. At the same time while the formation surrounding the well bore is being heated a gaseous stream containing-elemental oxygen, such as air, is introduced via the well bore into the formation. After a period of time the water in the aqueous solution containing the oxidation catalyst is evaporated, leaving behind a solid residue of the hydroxide oxidation catalyst introduced thereinto. This hydroxide residue serves to promote and better maintain the in situ combustion thusinitiated within the formation.

Still another method exemplary of the practice of this invention is to introduce into the formation a liquid petro leum fraction, preferably a coking petroleum residue or fraction, containing the oxidation catalyst dissolved or otherwise suspended therein. By this operation there is not only distributed within the formation an oxidation catalyst but also additional fuel, petroleum hydrocarbons and the like or finely divided carbon or coke, which may also be dispersed within the coking petroleum fraction for consumption by in situ combustion within the formation.

This application is related to the copending, was signed patent application Serial No. 624,998, filed November 29, 1956, in the names of Joseph C. Allen and Robert E. Kunetka, titled In Situ Combustion Within a Subsurface Formation Containing Petroleum Hydrocarbons. In this above-identified application there is disclosed an improved in situ combustion operation wherein oxygen or an oxidizing agent is employed or generated in situ in the in situ combustion operation to enhance or otherwise improve the in situ combustion operation.

As will be apparent to those skilled in the art many changes and substitutions are possible in the practice of this invention without departing from the spirit or scope thereof.

We claim:

1. A method of initiating or maintaining in situ combustion in a subsurface formation containing hydrocarbons which comprises introducing into said formation an aqueous solution of a water soluble inorganic compound as an oxidation catalyst, subjecting that portion of the formation into which said solution is injected to an elevated temperature sufficiently high to effect in situ combustion of the hydrocarbons therein while at the same time introducing into that portion of said formation a gaseous oxygen-containing combustion supporting stream, said gaseous stream being introduced into that portion of said formation into which said solution has been introduced and which is subjected to the aforesaid elevated temperature for a period of time suificient to effect evaporation of the water from said aqueous solution previously introduced into said formation to deposit within said formation a solid residue of said inorganic compound as an oxidation catalyst therein whereby in situ combustion of said hydrocarbons within said formation is carried out in the presence of the thus-deposited oxidation catalyst.

2. A method of initiating or maintaining in situ combustion in a subsurface formation containing hydrocarbons which comprises introducing into said forma tion an aqueous solution of a water soluble inorganic compound as an oxidation catalyst, said compound containing an element selected from the group consisting of potassium, sodium, lithium, barium and calcium, subjecting that portion of the formation into which said solution is injected to an elevated temperature sufficiently high to effect in situ combustion of the hydrocarbons therein while at the same time introducing into that portion of said formation a gaseous oxygen-containing combustion supporting stream, said gaseous stream being introduced into that portion of said formation into which said solution has been introduced and which is subjected to the aforesaid elevated temperature for a period of time suflicient to effect evaporation of the Water from said aqueous solution previously introduced into said formation to deposit Within said formation a solid residue of said inorganic compound as an oxidation catalyst therein whereby in situ combustion of said hydrocarbons within said formation is carried out in the presence of the thus-deposited oxidation catalyst.

3. A method in accordance with claim 2 wherein said gaseous stream is air.

4. A method in accordance with claim 2 wherein said References Cited in the file of this patent UNITED STATES PATENTS 1,806,499 Ranney et a1. May 19, 1931 1,870,320 Adams et a1. Aug. 9, 1932 2,423,674 Agren July 8, 1947 2,530,493 Van Loenen Nov. 21, 1950 2,722,277 Crawford Nov. 1, 1955 2,747,672 Simm May 29, 1956 

1. A METHOD OF INITIATING OR MAINTAINING IN SITU COMBUSTION IN A SUBSURFACE FORMATION CONTAINING HYDROCARBONS WHICH COMPRISES INTRODUCING UNTO SAID FORMATION AN AQUEOUS SOLUTION OF A WATER SOLUBLE INORGANIC COMPOUND AS AN OXIDATION CATALYST, SUBJECTING THAT PORTION OF THE FORMATION INTO WHICH SAID SOLUTION IS INJECTED TO AN ELEVATED TEMPERATURE SUFFCIENTLY HIGH TO EFFECT IN SITU COMBUSTION OF THE HYDROCARBONS THEREIN WHILE AT THE SAME TIME INTRODUCING INTO THAT PORTION OF SAID FORMATION A GASEOUS OXYGEN-CONTAINING COMBUSTION SUPPORTING STREAM, SAID GASEOUS STREAM BEING INTRODUCED INTO THAT PORTION OF SAID FORMATION INTO WHICH SAID SOLUTION HAD BEEN INTRODUCED AND WHICH IS SUBJECTED TO THE AFORESAID ELEVATED TEMPERATURE FOR A PERIOD OF TIME SUFFICIENT TO EFFECT EVAPORATION OF THE WATER FROM SAID AQUEOUS SOLUTION PREVIOUSLY INTRODUCED INTO SAID FORMATION TO DEPOSIT WITHIN SAID FORMATION A SOLID RESIDUE OF SAID INORGANIC COMPOUND AS AN OXIDATION CATALYST THEREIN WHEREBY IN SITU COMBUSTION OF SAID HYDROCARBONS WITHIN SAID FORMATION IS CARRIED OUT IN THE PRESENCE OF THE THUS-DEPOSITED OXIDATION CATALYST. 